1. Field of the Invention
The present invention relates to a method of and an apparatus for dressing tips for welding machines (hereinafter referred to as tips) wherein the tips are advanced toward a dresser body and are cut by the dresser body.
2. Prior Art
Japanese Patent Laid-Open Publication No. 4-127975 discloses a conventional method of and apparatus for dressing tips wherein when the tips are cut by a dresser body, the tips are advanced toward the dresser body to thereby press cutters of the dresser body whereby the cutters start to rotate. At this state, the tips are cut by the cutters while they press the dresser body for a given time, namely, under pressurized state. The tips are moved away from the dresser body immediately after the given time lapses and the cutters stop their rotation so that the dressing of the tips are completed.
This is described more in detail with reference to FIG. 6. In the same figure, a base 31 has rising portions 32 and 32 at both ends thereof. A pressure chamber 33 has shafts 34 and 35 which extend leftward and rightward therefrom. Each end of the shafts 34 and 35 is brought into contact with the rising portions 32 and 32. Each another end of the shafts 34 and 35 are housed in the pressure chamber 33 and always receives pressurized air in the pressure chamber 33 or pressing force of urged springs. A dresser body 36 has cutters 37 and 38 disposed at the tip end thereof, a box 39 disposed at the front portion thereof and having therein a drive mechanism (not shown) for driving the cutters 37 and 38, a known air motor (not shown) disposed therein for rotatably driving the cutters 37 and 38, and a connecting port (not shown) disposed at the rear end thereof and connected to a pressurized air supply pipe for actuating the air motor. The dresser body 36 has a through hole 40 bored therein. A holding shaft 41 penetrates the through hole 40 and has both ends which are respectively fixed to supporting members 42 and 42 respectively formed at both side surfaces of the pressure chamber 33. The holding shaft 41 has coil springs 43 and 43 which are wound thereon. The coil springs 43 and 43 are urged to press the dresser body 36. The pressure chamber 33 has switch holders 44 and 45 which respectively protrude from both side surfaces thereof. Switches 46 and 47 are respectively provided at the upper ends of the switch holders 44 and 45 and face side surfaces of the dresser body 36. The driving operation of the air motor is controlled by the switches 46 and 47.
Designated at 48 is a guide of the pressure chamber 33, and at 49 and 50 as illustrated by imaginary lines are tips to be dressed.
In case of dressing the tip 49, it is moved rightward in FIG. 6 so as to press the cutter 37 of the dresser body 36 at the tip end thereof. When the force of the tip 49 to press the cutter 37 (hereinafter referred to as pressing force) exceeds the urging force of the right coil spring 43, i.e. the force to urge the dresser body 36, the dresser body 36 is moved rightward and is brought into contact with the switch 46 at one side surface thereof so that the switch 46 is turned on. As a result, the pressurized air is supplied to the air motor by way of a control circuit, not shown, to thereby drive the air motor so that the cutter 37 rotates to dress the tip 49. Upon completion of the dressing of the tip 49, the tip 49 is moved leftward so that the pressing force of the tip 49 is released. Consequently, the dresser body 36 is moved leftward by the urging force of the right coil spring 43 so that the switch 46 is turned off. As a result, the pressurized air is not supplied to the air motor so that the cutter 37 stops its rotation.
However, when the shapes of the tips are greatly deformed at the time when the tips are dressed (refer to FIG. 4), for instance, when a mushroom-shaped projection 26 is formed at the tip end of the tip as illustrated in FIG. 4, the resistance of the tip against the cutter becomes large at the first stage of the dressing of the tip, whereby the cutter does not rotate even if the pressing force of the tip turns on the switch 46. Accordingly, the dresser body has not been effectively utilized.
The cutters normally comprise one blade or two blades configuration of which are conformity with recessed curved surfaces of the tips. There is such a problem that a stepped portion 27 remains on the curved surface of the tips upon completion of the dressing of the tip as illustrated in FIG. 5, which impedes the normal welding operation.
The present invention has been made in view of the problems set forth above and is to provide a method of and apparatus for dressing the tips wherein the cutters rotate before the tips are brought into contact with the cutters, then the tips are subjected to the first dressing, i.e. cut by the cutters and thereafter the tips are subjected to the last dressing so that the operation of the dresser body is assured and the stepped portions are eliminated from the curved surface of the tips.
To achieve the above object, the present invention comprises the steps of driving to rotate the cutters before the tips are brought into contact with the cutters, pressing the tips to the cutters, starting to dress, i.e. cutting the tips while the tips press the cutters, i.e. under pressurized state at a given time, moving the tips away from the cutters while the cutters continue to rotate and dressing the tips by gradually releasing the application of the pressure to the tips.
Accordingly, since the cutters normally rotate before the tips are brought into contact with the cutters of the dresser body, even if the deformed tips press the rotating cutters, the cutters do not stop their rotation whereby the normal dressing can be effected. Although the stepped portions are present on the surfaces of the tips which were cut by the cutters under pressurized state at a given time, the stepped portions are gradually cut by releasing the application of the pressure to the tips while the cutters continue to rotate.